內政部空中勤務總隊一架UH-1H直昇機於執行救生吊掛常年訓練時，在距地面約30呎，控制器向上操作之狀態下，發生鋼索無法控制而下滑，吊掛人員墜落地面受傷，依據我國飛航事故調查法規定，本次事件為一起飛航事故。飛航安全調查委員會為負責調查發生於中華民國境內之民用航空器、公務航空器及超輕型載具飛航事故之獨立機關，乃依據飛航事故調查法展開本次事故調查工作。調查結果發現：「事故吊掛機具於進廠翻修作業過程中，因軸向間隙值量測錯誤，組裝完成後造成耦合器之軸向間隙過大，於執行吊掛作業時，當驅動齒耦合長度由0.074吋逐漸降至0.015吋，其壁面承受最大應力超過降伏強度而破壞，驅動齒無法負荷從動齒的嚙合應力作用而滑脫，從動輪被負載帶動往反向旋轉，致使吊掛人員向下墜落。」本研究試圖由工程面向找出事故可能肇因，並導入材料試驗及有限元素分析等技術探討救生吊掛機具工程失效因素。首先審視原廠救生吊掛機具翻修作業內容及實際作業紀錄等資訊，同時藉由破壞形態觀察、顯微組織觀察、機械性質分析及有限元素分析驗證等項分析結果，以瞭解破壞的模式，解析失效之肇因。本文提出具體預防措施及改善建議，以避免類似失效再次發生。

A UH-1H helicopter of National Airborne Service Corps (NASC) performed the hoist up rescue training, the flight engineer released the wire rope and started to retrieve the rope to hoist personnel after seeing the end of the rope was hooked well with the trainee. Then the helicopter started moving forward slowly, and at the same time the flight engineer kept on retrieving the wire rope. At 30 feet from the ground the flight engineer felt the rope retrieving process was stopped and the rope started to slip down. After inspection flight engineer found that the pulling device could not be controlled, which led the rope to slip downwards and saw the hoisted personnel falling off to the ground. Due to Taiwan Aviation Occurrence Investigation Act, it was classed as an Aviation Occurrence. Taiwan Aviation Safety Council (ASC) shall be responsible to conduct the following investigations on aviation occurrence of Civil aircraft, Public aircraft or Ultra-light Aircraft arises in the territory of the Republic of China. Findings related to possible causes in ASC's final report: ＂During overhaul the hoist device had a wrong measurement for the axial gap value, which caused the axial gap of the coupling oversized after the assembly. During hoist operation when the coupling face length of the drive gear decreased from 0.074 inch to 0.015 inch, the maximum stress the drive gear wall could take was over the yield strength and damaged; the drive gear could not take the load of the coupling stress from the driven gear and began to slip. The driving gear was over-driven by the load to rotate in the opposite direction, which led the hoisted personnel to fall off.＂ This research intends to find the probable cause of the occurrence from engineering point of view, and proposes material test and finite element analysis (FEA) for Engineering Failure Analysis of the Rescue Hoist Device. At first, ASC checks all the maintenance records of the Rescue Hoist Device and makes sure that no abnormal was found. Following examinations and tests were macro observation and photographic documentation, chemical analysis, hardness testing, metallographic examination, Scanning Electron Microscope (SEM) examination, to determine the root cause of failure. Furthermore the finite element analysis is conducted for stress analysis. The sole purpose of this study is to give some preventions and safety recommendations, and ultimately prevent recurrence of similar failures.